The present invention relates to a backlight device that is used for a liquid crystal display or the like.
A known backlight device used for a liquid crystal display or the like is of an edge-lit type that is provided with a light source at a light incident face located at a side-edge part of a light guide plate.
For light weight and a narrow frame, such a backlight device is provided with a convex part at a part of one side face of the light guide plate, and the convex part is sandwiched between protrusions provided at a frame member for fixing.
For instance, a liquid crystal module disclosed in JP-A-2012-155236 (Patent Document 1) shown in FIG. 11 includes a rectangular convex part 113 at an end face of a light guide plate 102 as well as a pair of bulging convex parts 112A in the form of hollow bosses that is formed at a bottom plate 101b of a rear frame 101, so as to sandwich the convex part 113 between this pair of bulging convex parts 112A from both sides for positioning of the light guide plate 102.
The backlight device of an edge-lit type is configured to include a light-incident face of a light guide plate placed at a predetermined space from a light source such as a fluorescence tube or light emitting diodes (LEDs) disposed in a line. If this space is changed from the appropriate distance due to manufacturing error or displacement during operation, the brightness is lowered or its uniformity deteriorates unfortunately.
To solve this problem, a spread illuminating apparatus 240 disclosed in JP-A-2008-97877 (Patent Document 2) as shown in FIG. 12 includes a light guide plate 234 provided with protruding parts 242 each to be stored in the corresponding recess 244 of an inner frame member 236. The light guide plate 234 is housed inside the inner frame member 236 in such a manner that a part 242b of the protruding part 242 on the side opposite to the side of point light sources 212 is brought into contact with an elastic member 243 and so the light guide plate 234 is biased to the side of the point light sources 212 by pressing force F from the elastic member 243.
Thereby, the light guide plate 234 can be held in the inner frame member 236 while keeping necessary and appropriate clearance d, which is determined considering the extension and contraction balance depending on the physical properties of the materials of the light conductor plate 234 and the inner frame member 236 as well as dimensions in their extension directions.
In such a structure to hold a light guide plate, when the pressing force applied to the light guide plate toward the light source is changed, a distance between the light guide plate and the light source will change to affect the uniformity of brightness.
The spread illuminating apparatus 240 described in Patent Document 2 is configured to bias the light guide plate 234 by brining the elastic member 243 provided in the inner frame member 236 into contact with the protruding part 242, and so in the case of a structure to fix a light guide plate by the pair of bulging convex parts 112A provided at the bottom plate 101b of the rear frame 101 as in Patent Document 1, the elastic member 243 is fixed at a predetermined position and so the pressing force cannot be adjusted.
Then, it is an object of the present invention to provide an edge-lit type backlight device configured so that a distance between a light source and a light guide plate can be adjusted appropriately by adjusting pressing force applied to the light guide plate.